A typical internal combustion engine used in a vehicle includes some type of sensing assembly for measuring manifold absolute pressure (MAP) in order to determine the amount of pressure in an intake manifold, which is used by an engine computer to control some of the parameters of engine operation.
Also, in today's vehicles, during certain engine operating conditions, their is a desire to recirculate a portion of the exhaust gasses from the engine back into the intake manifold to mix with the incoming air. The amount of exhaust gas recirculation (EGR) is determined by an EGR valve, which is controlled by the engine computer. In order for the engine computer to determine if any change in flow of EGR gasses is needed it must have an input as to the current flow of EGR gasses. This is typically accomplished by locating an orifice in an EGR tube just downstream of the location where the EGR tube separates from the main exhaust stream, with taps into the EGR tube on either side of the orifice. The two taps are then connected to hoses leading to a relative pressure sensor that compares the upstream and downstream pressures to obtain the pressure difference. This value is then fed to the engine computer, and when combined with the MAP allows the engine computer to compute a delta pressure feedback exhaust (DPFE) signal, which is, in turn, used to determine the amount of EGR flow.
Several drawbacks to this technique of EGR sensing exist. One drawback is that there are two sets of taps and hoses needed to obtain the pressure value, in addition to an entirely separate sensor assembly for reading the MAP pressure. Further, with the location of the orifice, and corresponding taps and hoses, being close to the main exhaust stream, the sensor assembly is exposed to a great deal of heat from the exhaust gasses, and so relatively expensive materials must be employed to withstand this heat and operate adequately during the life of the vehicle. Also, the sensor assembly can be affected by the pressure pulses in the exhaust stream.
An additional sensing system that is coming into wide use in vehicles today is an electronic returnless fuel system. In order to operate this system effectively, a sensor assembly must be employed at some point in the fuel system to monitor the fuel pressure. Typically, this fuel pressure sensor system involves a differential pressure sensor employed with taps and hoses extending from both the fuel rail and the intake manifold in order to obtain a value as to the difference in pressure between the two. With this arrangement, hot fuel is contained within one of the pressure hoses, which is generally not desirable, and further, a rather more complex differential pressure sensor is employed to obtain the needed pressure measurement.
Thus, there are several separate sensing assemblies in vehicles, all directed toward controlling some portion of the total intake of gasses and fuel into the engine, each of which adds to the cost and complexity of the overall engine assembly. Consequently, a desire exists to have an inexpensive and reliable sensing system for accurately monitoring the intake of gasses and fuel into the internal combustion engine.